September 2018 Business Due Dates

September 17 - S Corporations

File a 2017 calendar year income tax return (Form 1120S) and pay any tax due. This due date applies only if you requested an automatic 6-month extension. Provide each shareholder with a copy of K-1 (Form 1120S) or a substitute Schedule K-1.

September 17 - Corporations 

Deposit the third installment of estimated income tax for 2018 for calendar year

September 17 -  Social Security, Medicare and withheld income tax

If the monthly deposit rule applies, deposit the tax for payments in August.

September 17 - Nonpayroll Withholding

If the monthly deposit rule applies, deposit the tax for payments in August.

September 17 - Partnerships

File a 2017 calendar year return (Form 1065). This due date applies only if you were given an additional 5-month extension. Provide each partner with a copy of K-1 (Form 1065) or a substitute Schedule K-1.

September 17 - Electing Large Partnerships 

File a 2017 calendar year return (Form 1065-B). This due date applies only if you were given a 6-month extension. March 15 was the due date for furnishing Schedules K-1 or substitute Schedule K-1 to the partners.



Share this article...

Want our best tax and accounting tips and insights delivered to your inbox?

Sign up for our newsletter.

I confirm this is a service inquiry and not an advertising message or solicitation. By clicking “Submit”, I acknowledge and agree to the creation of an account and to the and .

Our Offices

Our expertise is widespread and we have multiple office locations to make it convenient for you to get help. You can find us at:

Oregon Office

4545 SW 96th Ave
Beaverton, Oregon 97005
Monday through Friday:
9am to 5pm and by appointment

April-December
Monday through Thursday
10am to 2pm

Connecticut Office

P.O. Box 271356
West Hartford, Connecticut 06127
By Appointment Only

Idaho Office

2020 Blaine St.
Caldwell, Idaho 83605
Monday through Friday:
9am to 5pm and by appointment

April-December
Monday through Thursday
10am to 2pm